It has been reported that the Application menu on MacOS cannot be localized using the Engine. It appears that when the Engine creates this menu, it does not use the localization system in the Engine.
1. Open editor Preferences -> Region
2. Change editor language
3. Mac Menu text items should update with the localized text items if they exist.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-49526 in the post.